CVE-2025-38250

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: hci_core: Fix use-after-free in vhci_flush()

syzbot reported use-after-free in vhci_flush() without repro. [0]

From the splat, a thread close()d a vhci file descriptor while

its device was being used by iotcl() on another thread.

Once the last fd refcnt is released, vhci_release() calls

hci_unregister_dev(), hci_free_dev(), and kfree() for struct

vhci_data, which is set to hci_dev->dev->driver_data.

The problem is that there is no synchronisation after unlinking

hdev from hci_dev_list in hci_unregister_dev(). There might be

another thread still accessing the hdev which was fetched before

the unlink operation.

We can use SRCU for such synchronisation.

Let's run hci_dev_reset() under SRCU and wait for its completion

in hci_unregister_dev().

Another option would be to restore hci_dev->destruct(), which was

removed in commit 587ae086f6e4 ("Bluetooth: Remove unused

hci-destruct cb"). However, this would not be a good solution, as

we should not run hci_unregister_dev() while there are in-flight

ioctl() requests, which could lead to another data-race KCSAN splat.

Note that other drivers seem to have the same problem, for exmaple,

virtbt_remove().

[0]:

BUG: KASAN: slab-use-after-free in skb_queue_empty_lockless include/linux/skbuff.h:1891 [inline]

BUG: KASAN: slab-use-after-free in skb_queue_purge_reason+0x99/0x360 net/core/skbuff.c:3937

Read of size 8 at addr ffff88807cb8d858 by task syz.1.219/6718

CPU: 1 UID: 0 PID: 6718 Comm: syz.1.219 Not tainted 6.16.0-rc1-syzkaller-00196-g08207f42d3ff #0 PREEMPT(full)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025

Call Trace:

<TASK>

dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120

print_address_description mm/kasan/report.c:408 [inline]

print_report+0xd2/0x2b0 mm/kasan/report.c:521

kasan_report+0x118/0x150 mm/kasan/report.c:634

skb_queue_empty_lockless include/linux/skbuff.h:1891 [inline]

skb_queue_purge_reason+0x99/0x360 net/core/skbuff.c:3937

skb_queue_purge include/linux/skbuff.h:3368 [inline]

vhci_flush+0x44/0x50 drivers/bluetooth/hci_vhci.c:69

hci_dev_do_reset net/bluetooth/hci_core.c:552 [inline]

hci_dev_reset+0x420/0x5c0 net/bluetooth/hci_core.c:592

sock_do_ioctl+0xd9/0x300 net/socket.c:1190

sock_ioctl+0x576/0x790 net/socket.c:1311

vfs_ioctl fs/ioctl.c:51 [inline]

__do_sys_ioctl fs/ioctl.c:907 [inline]

__se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]

do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94

entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7fcf5b98e929

Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007fcf5c7b9038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010

RAX: ffffffffffffffda RBX: 00007fcf5bbb6160 RCX: 00007fcf5b98e929

RDX: 0000000000000000 RSI: 00000000400448cb RDI: 0000000000000009

RBP: 00007fcf5ba10b39 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

R13: 0000000000000000 R14: 00007fcf5bbb6160 R15: 00007ffd6353d528

</TASK>

Allocated by task 6535:

kasan_save_stack mm/kasan/common.c:47 [inline]

kasan_save_track+0x3e/0x80 mm/kasan/common.c:68

poison_kmalloc_redzone mm/kasan/common.c:377 [inline]

__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:394

kasan_kmalloc include/linux/kasan.h:260 [inline]

__kmalloc_cache_noprof+0x230/0x3d0 mm/slub.c:4359

kmalloc_noprof include/linux/slab.h:905 [inline]

kzalloc_noprof include/linux/slab.h:1039 [inline]

vhci_open+0x57/0x360 drivers/bluetooth/hci_vhci.c:635

misc_open+0x2bc/0x330 drivers/char/misc.c:161

chrdev_open+0x4c9/0x5e0 fs/char_dev.c:414

do_dentry_open+0xdf0/0x1970 fs/open.c:964

vfs_open+0x3b/0x340 fs/open.c:1094

do_open fs/namei.c:3887 [inline]

path_openat+0x2ee5/0x3830 fs/name

---truncated---